Communication channel identification in telephone or like systems



April 3, 1951 Filed Jan. 24, 1948 G. COMMUNICATIO F BELLAIRS IN TELEPHONE 0R LIKE SYSTEMS ET' AL N CHANNEL IDENTIFICATION 4 Sheets-Sheet l April 3, 1951 Filed Jan. 24, 1948 coMMuNlc G F. BELLAIRS ETAL TION CHANNEL IDENTIFICATION IN TELEPHONE 0R LIKE SYSTEMS 4 Sheets-Sheet 2 April 3, 1951 G. F. BELLAlRs Erm. 2,547,517

COMMUNICATION CHANNEL IDENTIFICATION IN TELEPHONE 0R LIKE sYsTENs Filed Jan. 24, 1948 4'Sheets-Sheet 3 April 3, 1951 G. F. BELLAIRS :TAL 2,547,617

vCOMMUNICATION CHANNEL IDENTIFICATION IN TELEPHONE on LIKE SYSTEMS Filed Jan. 24, 1948 4 Sheets-Sheet 4 F15-'5- r- *Fg M/ 1F fr pfz 11m f xz I i I ff r4 I R3 I DR I l I l I V c 's0' 'W2 I l I l M I I Cl'A r I I I I M2 l l M6 l I K2 I I V"\/f\2 I BPM M5 I I II I' gna I l L J I As K1 l M5 i 1| Le@ I If: I M4 Pf D572 K l `I )A l l CC/ I| I I: M/ /f Bfr I I l l i l D@ I Il LFH vo m A4 50 i J Patented Apr. 3, 1 951 COMMUNICATION CHANNEL IDENTIFICA- TION IN TELEPHONE ORLIKE SYSTEMS Guy ffarington Bellairs,

London,A and. John Charles Ireland, Tunbridge Wells, Kent, England,

assgnors to British Telecommunications" Research Limited, Taplow, England, a British Applicationl January 24, 1948, Serial No. .4,147 In Great Britain January 27, 1947 (Cl. 179-15 )l 7 Claims.

This invention relates to telephone and like systems. MoreA particularly it is concerned With telephone or like systems of the kind in which calls are set up automatically over carrier frequency channels which will be referred to as communication channels.

According to a feature of the invention in order to identify a communication channel over which a connection is set up frequency ascertaining means by which the individual characters designating the communication channel are successively identied are associated with a point to which a frequency characteristic of the communication channel is adapted to beconnected up when it is desired to ascertain the identity of the communication channel.

The connecting up may be effected automa-tically by equipment individually associated with the communication channel.

It may be desired to identify communication channels over which connections are set up for a variety of purposes such as traiic analysis and especially metering. In the latter case the connecting up of the characteristic frequency may be initiated on the response of a called substation.

The frequency ascertaining means may cause the operation of a meter associated with the calling substation by the use of conventional marking out circuits, or it may cause the marking or punching of a common recording means Witha sign or signs characteristic of the calling substation.

Various metho's of identifying the frequencyr of the communication channels are possible.

According to a second feature of the inventionl in an arrangement for identifying the individual characters of the'designation of a characteristic frequency of a communication channel over which a connection is set up in a telephone or like system, a wave of the characteristic frequency or of a frequency derived therefrom is led to a set of parallel connected filters, whose pass bands together cover the possible range of frequencies which may be fed to the filters for identifying the rst character, each filter having an individual responding device associated therewith, each of said lters is followed by a frequency'changer tobring the combination frequencies obtained from all theA mixers to a common frequency range, reduced as compared with the frequency range of' the waves which may be fed to the filters, and the said combination frequencies falling within the reduced frequency range are fed to another set of parallel connected filters whose pass bands together cover the reduced frequency range and each of which has an individual responding' device associated therewith, whereby a further character designating the communication channel may be identified.l

According to a third feature of the invention in an arrangement for identifying a characteristic" frequency of a communication channel over which al connection is set' up in a telephone or like' system, sets of reference frequencies one set for each character designating a communication channel are adapted to be connected up successively to be mixed in turn with av wave of the characteristic frequency or of a frequency derived therefrom so that successive resultant combination waves are enabled to pass a filter device and operates a responding device whereby successive characters designating the characteristic frequency or a group to which the characteristic frequency belongs is identified by the reference frequencies thus connected up.

According to a fourth feature of the invention in an arrangement for identifying a characteristic frequency of a communication channel over which a connection is set up in a telephone or like system in which the characteristic frequencies can be made up by mixing frequencies corresponding to the individual units, tens, etc., digits of the number of the corresponding stations, the characteristic frequency is successively mixed with waves of frequencies of a set' of equally spaced reference frequencies corresponding to the possible first digits of the numbers which identify the communication channels until the combination frequency produced passes through a low-pass (or other) lter to signify the identification of the first digit `whereupon the said combination frequency is successively mixed with waves of frequencies of a second set of equally spaced reference frequencies correspending to possible second digits, of the said numbers, until the further combination frequency produced passes through a filter to sigso on until all the digits corresponding tc the numbers of the calling communication channel have been identified.

The sets of frequencies corresponding to the digits of the numbers which identify the cornmunication channels may be generated by frequency multiplying from a common master oscillator. Alternatively they may be generated by variable oscillators.

The invention will be better understood from the following description of possible arrangements for carrying it into effect.

Fig. 1 shows a frequency ascertaining means.

Fig. 2 shows a second frequency ascertaining means. Y

Fig. 3 shows a third preferred form of frequency ascertaining means.

Fig. 4 shows a metering arrangement in association with the other exchange apparatus necessary for its understanding.

Fig. 5 shows a development of Fig. 4 to provide a multi-metering arrangement.

Fig. 1 shows an arrangement in which a plurality of parallel connected filters F are provided, each filter passing one of the communication channel frequencies so that if a particular communication channel frequency is received a detector device D associated with the appropriate lter will be operated.

When dealing with a large number of communication channels, e. g. 500, the cost of the filters or difficulty in design may come into consideration and an arrangement such as that shown in Fig. 2 may be appropriate.

Fig. 2 shows five lters IFI, IF2, IF3, 1F15 and IFS which divide the frequency range corresponding to the 500 communication channels into five parts each corresponding to a 100 channels and each being dealt with by the appropriate filter. When a communication channel frequency is passed through one of the filters the associated responding or detector device D is operated and the frequency is extended to corresponding mixer M and filter F. The five mixers M are each fed with frequency respectively, Fri, FrZ, FTB, Fr and Fr5, which are so arranged as to translate each of the five frequency ranges above mentioned into one common secondary frequency range.

The combined output of the filters F is passed to ten parallel connected lters 2F@ to ZFQ.

When a communication channel frequency which will have been translated into the common secondary frequency range is received it will pass through the appropriate one of the filters 2F@ to EFS) and operate the corresponding detector DI. It will also be passed to a mixer Mi associated with the particular filter.

A set of frequencies Fii to Frl are respectively fed to the mixers Ml and the values of these are arranged so that the frequencies passing the respective filters 2F! to 2F53 are translated into one common tertiary frequency range.

After filtering by the low pass filter Fi the combined output is now fed to a series of filters SFS to SFS.

When a communication channel frequency (which will have been translated into the cominon tertiary frequency range) reaches these filters it will pass the appropriate one and operate the corresponding detector D'.

Thus three detectors will be operated one cach ofthe sets D, Dl and D2 and will give a complete identification of the communication channcl frequency which has been fed to the equipment.

A suitable frequency allocation of the arrange- Pass rango in 1n c g a c yl c s, per second Filter be as follows:

l Frequency in i megacycles per second The filter F would pass all frequencies of 17.952 megacycles per second and below, and the filters F1 would pass all frequencies of 1.632 megacycles per second and below. The filters F, Fi could in fact however be dispensed with with the frequency values given above.

In the arrangements of Figs. 1 and 2 it will now be apparent that the characteristic frequencies are made up by mixing frequencies corresponding to the individual units, tens and hundreds digits of the number of the corresponding station. Such an arrangement however is not the only possible one and instead of this which is a decade system of identification, some other system such as binary system might be used.

A further saving in equipment in the frequency ascertaining arrangement might be effected if instead of providing a number of mixers at each stage to which fixed frequencies are connected, a single mixer were provided and a set of frequencies arranged to be connected in rotation to the modulator until the appropriate frequency to pass on the incoming wave is found.

Fig. 3 shows such an arrangement. An incoming frequency connected to the point I is fed to a mixer Ml. A series of equally spaced frequencies 00 to 09 are fed in turn to the mixer Mi according to the position of a ten-way switch SI until the correct frequency is found to give a single combination frequency .coneidered in connection with .which .will pass the filterv Fl tol be detected by a detector DI and operate a relay Rl or other appropriate device. The detector DI and relay Rl constitute a responding device and serve to cause the arrest of the wipers SI. The output of the lter FI is also extended to a miXerM to which the frequency of a second set of equally spaced frequencies 000 to 009 may be connected in turn by the operation of a ten-Way switch S2, which is started up by the operationl of relay Rl untill the appropriate combination frequency is produced to passa filter F2 and be detected by a detector D2 to operate a relay R2 or other device which serves to arrest the wipers of S2. The output of F2 isffed to a third mixer M3 to -which the frequencies of a third set ofv equally spaced frequencies 0000 to 0009 can be con nected one at a time by operation of a ten-way switch S3y which is started up by the operation of relay R2 until the appropriatel combination frequency is produced to be detected by a. detector D3. and operates relay R3 0r other device which, serves to arrest the wipers ofV S3. The frequency range of the second set of frequency 0.00. to 009 is chosen to fall withinV the frequency interval of the rst set 00 to 009 and the. fre.- quency range of the third set 0000 to 0009 is chosen to fall within the frequency interval of the second set.

The ten-way switches might be mechanical switches or a series of gas discharge triodes adapted to .be consecutively triggered.

The frequencies foruse in connection with the apparatus of Fig. 3 for the identification of a discrete frequency from the same series as was Fig. 2 might be as follows:

Frequency l Y in mega cycles per second The filter Fl would then pass frequencies of 17.952 megacycles per second and below, the filter F2 frequencies of 1.632 megacycles per second and below; and the filter F3 frequencies of 8 kilocycles per second and below.

".n place ci" switcher 'Meri f" e icy ies, ne provided Variable s^ e `...car that uency osciln "lat-ors or other sources each adapted to be set Ato produce any one of ten discrete frequencies `acteristic or variable frequency filters each adapted to seone of ten discrete frequencies simultaneously applied to them.

in certain` circumstances only one frequency will be ied to the frequency ascertaining means at a time but in other circumstances more .than one frequency is likely to be present simultane ously especially where for economy one frequency ascertaining` means is employed to meter a large number of independent equipments. In such circumstances a form of frequency finder wiily be necessary to ensure that only one of the frequencies is pici'zed up at a time and fed to tre frequency identifying device. f

A suitable frequency finder is that described` in our copending application Serial No. 4143, filed January 24. 1943. is used in connection with the present ini ntion this frequency finder covers a given frequency range and when a charfrequency in this range is fed to it, it sets itself to lock in to the characteristic frequency and remains locked in until the fre quency has been identified by the frequency ask cer-taining means. it is then released and f to anotizier characteristic frequency i rlich may be connecte-i to it.' details of i-he irefuency iinder will.' appear from the followingv desuiption.

Fig; shows the essential details of the fre'- quency finder connected in circuit for the purpese. of finding meteringr freguencies in .a tele-` phone system of th kind described in `our copen-ding applicatin Serial 41.43, filed January 24, 1943'.

CCiB is a trans-mission. path over which carrier frequencies are received and are .searched for by a frequency finder FFE'. The method of searching is to use a sweep oscillator SOto control the frequency of a variable scillator VO by meansof a controldevice CD which may be a v reactance valve. The frequency irornthevariable oscillator isfed to a mixer Mi. together with any incoming frequency over transmission path CCIE. When an incoming frequency beats with the variable osciliator frequency to give a signal which passes the intermediate filter device EF. the signal is detected by the detector DET and inserat-'Sy the relay A and is also passed to the discriminator DSC, which also controls the controlA deviceCD. Contact A! of the relay A disconnects the sweep oscillator SO, and the control dei/*ice CD cornes under the control of the discriminator DSC which controls CD, so as to set the variable oscillator to a frequency value. which wi'il. gire a signal near the iniddle of the pass band ofthe intermediate iilter IF.

Contact A? of the relay A connects the variable osciliator frequency to a mixer M2 and also under the control of Contact Di reiay D (not shown) which responds on reply of a calied subscriber and Contact of relay to a metering frequency fin-der FF? which operates generally in the same. ina-nner as the frequency under bute/ith differences which will be described later.

The miner M2 passes the Variable oscillator' irefiuencJ to the return transmission path CCIA.

when relay IJy subsequently operates due to re'fly of the caiied su? tation as described 'e in cui.' cop-enx ne eppiication Serial i d anuary 241.1048. frequency of the lia-tor VG wiil be connected to the ng point and the currency finder r proceed to iind the freeuency of the 1' vwreabl'e oscillator` VO", in the saine lmanner asis described for frequency finder FFE.

When relay A which corresponds to relay A in frequency finder FFI operates its contact A2 connects up frequency identifying metering equipment ME, which may be of the kind shown in Fig. 3 for example.

The identification of the frequency may be arranged to control the operation of a meter corresponding to the substation to which the frequency identified has been assigned for calling purposes or it may be caused to influence the recording on a tape or punched card or the like of the number of the substation whose frequency has been identified or otherwise used for charge assessing purposes.

When the frequency has been identied and the charge assessing apparatus operated it is arranged that a relay Z is operated and closes its contact ZI.

A xed oscillator FOgenerates a frequency of 2,600 cycles which is fed to a mixer M3. With contacts Z and AS closed this Ywill beat with the incoming frequency from the metering point MP and a metering acknowledge frequency will be passed to the metering acknowledge point MAP (which may be common to a number of frequency fin-ders such as FFI i Thence the metering acknowledge frequency is passed to a, mixer M4 where it beats with the frequency from the variable oscillator VO', to

give a 2,000 cycle beat note which passes the low pass filter LPF and reaches the detector DET2 to bring about operation of relay K over its lower winding. Relay K locks up over contacts A3 and Ki and at contact K2 disconnects the frequency finder FF! from the metering point MP.

Relay A and relay Z will be restored and the frequency finder FFZ will thus be freed to operate to pick up other frequencies which may be connected to the metering point MP.

It will be understood that the characteristic frequency may be reconnected up at predetermined intervals while a connection exists over the communication channel so that time metering is effected.

While the above has described how single-fee metering will be effected, it will further be shown how multi-fee metering may be effected.

Fig. 5 indicates how this can be done by modulating the frequency identifying the calling subscriber with a low frequency. There is shown the essential part of the frequency finder FFI of Fig. 4 and also the part of an exchange selector WLS, essential for understanding the functioning of the multi-metering equipment. VThe selector WLS is a modification of the exchange selector' described more fully in our copending application Serial No. 4,143, filed January 24, 1948.

The metering frequency nder FP2 is arranged very much the saine as in Fig. 4 except that it is adapted to accept modulated waves whose modulation frequency corresponds to the amount of the fee to be recorded against the wave in question. To effect this discrimination, in addition to the variable oscillator VO of Figure 4 which finds the carrier frequency corresponding to the calling station, the detector DETI feeds the demodulated frequency from Ml and IFI to three band pass filters BPFi, BPFZ and BPF3 and these respectively feed the detectors DET2, DET3 and BETA each of which controls the operation of a relay or other device, respectively Rl, R2 and R3 in the multi-metering frequency ascertaining equipment MME, the arrangement of which will be described later.

In the exchange selector WLS there is shown one of a number of xed frequency marker oscillators MO connected to the marker test point,

Vone of which oscillators will correspond to each channel in the transmission path over which the connection is outgoing either permanently or under control of impulses dialled for setting up a connection.

Each marker oscillator frequency is displaced from the carrier frequency of the channel to which it applies by a small amount which may have one of three values according to whether the use of its channel is required to effect recorda low frequency through the band pass filter BPF corresponding to the amount of displacement to mixer M which is an additional mixer provided in the frequency nder FFl but which might in fact be incorporated with mixer M2. This low frequency corresponds to the frequency displacement of the marker oscillator MO and is therefore a measure of the fee to be recorded.

To mixer Mi will also be fed the frequency of the variable oscillator VO of the frequency finder FF! and the resulting beat frequency, which frequency will be characteristic of the calling line and of the fee to be charged, will be fed to the metering point MP via contact Di when the called subscriber replies, and will be picked up by the frequency finder FP2 in the manner previously described.V The mixer Ml serves to separate the carrier frequency charaeterising the calling line from the demodulating frequency characterising the fee and assuming the frequency displacement of the oscillator MO corresponds to a double fee the corresponding relay R2 will be operated and this in conjunction with the frequency identification over the lead which is extended over contact AZ to the multi-metering equipment will bring about the twofold operation of the corresponding subscribers meter, alternatively a common record can be marked up with the subscribers identification and the fee.

It will be appreciated that instead of providing a number of marker oscillators of differing frequency displacement it would be possible to provide marker oscillators which emitted a number of pulses in accordance with the fee to be charged, which pulses would be separated out in the metering equipment.

It will also be appreciated that in order to effect metering in accordance with the dui'ation of a call it would be possible to feed the metering frequency to the metering point MP again at say three minutes intervals during the period in which the connection is in being.

We claim:

l. In a telecommunication system, a carrier frequency identifying arrangement comprising a rst identifying means for ascertaining a first character designating a carrier frequency, a second identifying means for ascertaining a second character designating a carrier frequency, a first enabling means whereby the first identifying means is caused to become operative to ascertain the first character of a particular carrier frequency, a second enabling means made operament as claimed in claim 1,

tive by said first identifying means when said first character has been ascertained for enabling said second identifying means to become operative to identify the second character of said carrier frequency, whereby the characters designating said carrier frequency are ascertained successively and automatically.

2. A carrier frequency identifying arrangement as claimed in claim 1, in which the first enabling means comprises a switching device by which the carrier Wave Whose frequency is to be identiiied is connected upy to the first identifying means.

3. A carrier frequency identifying arrangement as claimed in claim 2, in which a disabling device is provided which is operated when the identification of the carrier frequency is complete to render said switching device no longer effective and to cause an indication to be given corresponding to the identification which has been ascertained.

4. A carrier frequency identifying arrange-a in which the first enabling' means comprises a frequency hunting device including a, variable with arresting means which, when the carrier frequency to be identified is found, generates a Wave of the same frequency for connection to the first identifying means.

5. A carrier frequency identifying arrangeh`y ment as claimed in claim 4, in which the rst enabling means include filter devices and responding devices associated with each lter device by which different modulations of the cairier frequency can also be identified.

6. An arrangement for identifying the characters designating a frequency characterising a communication channel in a telecommunication system comprising a first identifying means including a first set of parallel-connected lters, each iilter of the first set having a pass band which is distinctive for each of a plurality of first characters used for part 0f the designation of a carrier frequency, a set of individual first responding devices, each being correlated with a distinctive one of the filters of said first set, a second identifying means also including a second set of parallel-connected iilters, each filter of said second set having a pass band which is distinctive for each of a plurality of second characters used for another part of the designation of a carrier frequency, the total range of the pass bands of the second set of filters being less than the pass band of a single iilter of the first set and the set of individual second responding oscillator, together devices each being correlated with a distinctive one of the filters of the second set, a first enabling means whereby a carrier frequency is applied to the first identifying means to cause one of said first responding devices to operate to identify the first character of the designation of said carrier frequency, and a second enabling means made effective by said first identifying means to cause one of said second responding devices to operate to identify the second character of the designation of said carrier frequency.

7. Anarrangement for identifying the characters designating a carrier frequency characterising a. communication channel in a telecommunication system, ccmprising a plurality of identifying means, each including a set of sources of 1 waves, each wave of each source of each set having a different frequencyand each set having sources of waves of frequencies which are distinctive for the dierent part of the designation of a carrier frequency, while each` source in each set is distinctive y,of one of the lcharacters representing that part of the designation, a wave frequency mixing means, progressively operated means for connecting the sources of the set to which it belongs to the Waver'frequency mixing means of that set, filter means connected to the outlet of the mixing means and lresponding devices connected to the outlet of said iilter means, the outlet of the filter means of one set being connected to the mixing means of a. succeeding set except the last, and means for causing the successive operation of the progressively operated means of each set and effecting their arrest by the responding devices ofthe respective sets until characters representing the whole of the designation of a carrier frequency are identified.

' GUY FFARINGTON BELLAIRS.

JOHN CHARLES IRELAND.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

